Fused electrical plug

ABSTRACT

A dead front, back-wired electrical plug having a front accessible fuse mounted in a fuse well in the front face, a pivotable safety cover on the front face swingable into covering and uncovering relationship with the well, and a hollow plug housing with back-wired terminal posts for the respective contact blades and ground pin which project from the front face.

[ Aug. 13, 1974 United States Patent 1191 Eckart FUSED ELECTRICAL PLUG[75] Inventor: George R. Eckart, Lake Zurich, Ill.

Daniel Woodhead Inc, Northbrook, Ill.

Assignee:

ll/l922 Great Britain 339/44 M 122 Filed: 01.30, 1972 21 App]. No.:302,230

Primary ExaminerRichard E. Moore Attorney, Agent, or Firm lohnston,Keil, Thompson & Shurtleff 339/206 P H0lr 13/58, HOlr l3/68 ABSTRACT I[58] 337/196 339/39 44 A dead front, back-wired electrical plug having afront 339/1'47 206 accessible fuse mounted in a fuse well in the frontface, a pivotable safety cover on the front face swingable into coveringand uncovering relationship with the well, and a hollow plug housingwith back-wired terminal posts for the respective contact blades andground pin which project from the front face.

[56] References Cited UNITED STATES PATENTS l,92l,447 8/1933 Barnett339/63 R 1,974,790 9/l934 Barth 339/63 R 2,636 097 4/l953Shapiro........,...... 337/201 X 8 Claims, 8 Drawing Figures FUSEDELECTRICAL PLUG The invention herein concerns improvements in fusedelectrical'plugs, particularly those having a dead front and back-wiringof the terminal posts of the blades and ground pin, having a well for afuse in the front face of the plug, the well having a safety covermovable into and out of covering relationship with the well. The fuse isconnected in the plugs circuit between a terminal post and its contactblade. Other improvements of the invention reside in the configurationof the contact blade-mounting block to provide a compact assembly of thefuse contacts, the contact blades, the ground pin and the terminal posttherefor.

A fused plug will protect motors, test instruments, data processingequipment, and other similar machines or equipment against damage causedby brown-outs, unexpected voltage drops or other electricalmalfunctions. The amperage reading for the fuses may be tailored to thesafety needs for each particular motor, instrument, piece of equipment,or machine, e.g., over a fuse range of 0.25 amps.

The location of the fuse well in the dead front of the I plug and theprovision of a fuse well cover on the dead front has several advantages.For added safety, the fuse can be removed only after the plug has beenremoved from the receptacle. When removed, the cover plate is readilymoved into and out of covering relationship relative to the fuse wellwhereby fuses-may be quickly checked or replaced.

One previously known type of fuse plug is a frontwired plug in which theterminal posts for one contact blade and the ground pin are recessed inforwardly opening wells immediately behind the front face of the plug.The terminal post for the other contact blade is positioned in a fusewell located next to the aforesaid wells. One of the fuse clips iselectrically connected with the latter terminal post, while the otherfuse clip is electrically connected with the latter blade.

The front face of said known plug is a removable dielectric cover platewith openings for the contact blades and ground pin. A body with acylindrical passage is integrally molded on the back face of thedielectric cover plate. This body holds the midportion of a cylindricalfuse and slips between the fuse-mounting clips in the well when thecover plate is slid over the blades and ground pin and mounted on theplug body. The

THE INVENTION HEREIN This invention provides improvements over the knownfused electrical plug described above and other fusing arrangements forelectrical plugs by providing a dead front, back-wired electrical plugwith a frontaccessible fuse. The plug of the invention comprises ahollow plug body of dielectric material with a blademounting body ofdielectric material mounted in one end of the hollow plug body. Theblade-mounting body has electrical contact blades, and optionally aground pin, projecting from its front face, which also serves as thefront face of the plug. The plug has circuit means for connecting itsblades to the current wires of an electrical cord or cable and, whereprovided, for connecting the ground pin to the ground wire of such cordor cable.

The circuit means includes a fuse in the circuit for the blade connectedto the hot wire. This fuse is located in a well in the front face of theplug. Two fusemounting clips are seated in the well. A cover member ofdielectric material is mounted on the front face of the plug and ismovable into and out of covering relationship with relation to the well.

Preferably. the cover member is a thin plate of dielectric materialconnected by pivot means to the front face providing for the swinging ofthe cover member into and out of covering relationship with the well.The pivot means advantageously is provided with an arm projecting fromthe side of the thin plate, the base of the arm being pivotallyconnected to the front face.

The terminal posts for the respective blades and ground pin are locatedon the rearward side of the blade-mounting body. These terminal postsare seated in wells or recesses in the rear face of the blademountingbody. A separable cap covers the rear face and the wells or recessestherein to keep the bare ends of the wires well separated and isolatedwhere they are attached to the respective terminal posts. The cap haspassages or apertures through which the wires can pass into therespective wells or recesses.

The rearward end of the plug has a clamp for securely clamping thesheathed portion of the electrical cord or cable for the plug. Suchclamp preferably has one section integrally molded with the rear portionof the hollow body of the plug and a removable section attached by boltsto the first-mentioned section. The cord is clamped between the sectionsby a bevelled, arcuate wall provided in the clamping face of thefirstmentioned section and a pair of arcuate walls provided in theclamping face of the removable section. These arcuate walls accommodatecords or cables of various sizes and securely clamp such cords or cablesby a biting action of the respective arcuate walls into the outer,insulated sheath of such cords or cables.

THE DRAWINGS A preferred embodiment of the invention is illustrated inthe drawings, wherein:

FIG. I is a rear perspective view of the embodiment with the removable,electric cord or cable-clamping member also shown in phantom in explodedposition;

FIG. 2 is a front perspective view of the embodiment with the coverplate for the fuse well in closed position;

FIG. 3 is a view similar to FIG. 2 with the cover plate in open positionand the fuse in exploded, perspective view;

FIG. 4 is an exploded, front, perspective view of the three majorcomponents of the electrical plug, i.e., the hollow plug body, thecontact blade-mounting block, and the removable electrical cable or cordclamp member;

FIG. 5 is an exploded, rear perspective view of the blade-mountingblock, and its rear cap with one contact blade and the ground pin inexploded view and the other contact blade mounted in the block;

FIG. 6 is an exploded, front perspective view of the contactblade-mounting block with the other contact blade, its terminal postassembly, and the fusemounting clips in exploded view;

FIG. 7 is a side plan view of the blade-mounting block as viewed fromplane 77 of FIG. 2; and

FIG. 8 is a schematic diagram of the wiring of the electrical componentsof the plug.

THE ILLUSTRATED EMBODIMENT The electrical plug 10 has as its maincomponents a dielectric hollow plug body 11 made of an opaque,translucent or transparent thermoplastic or thermosetting syntheticpolymer and a dielectric, contact blademounting block 12 molded fromlike or different thermoplastic or thermosetting synthetic polymer,e.g., Lexan (trademark), a polycarbonate polymer or resin. The block 12has a dead front face 13. The so-called dead face results fromback-wiring of the rearwardly located terminal posts 16 and 17 for thecontact blades 14 and which project from the dead front face. The groundpin 18 also projects from the front face with its terminal post 19 alsobeing back-wired.

The block 12 fits into the end 20 of the plug body 11 with its groove 21mating with the internal rib 22 in the body 11. The block has ablade-accommodating passage 23, a ground pin-accommodating passage 24,and a blade-accommodating slot 25. The latter extends transverselyacross the inner side wall 94 of a fusereceiving well 95 extendinglongitudinally along one side of the front face.

The blade 14 lies in slot 25. Its base has a diagonal leg 26 and anapertured car 27. The latter is conductively connected by rivet 28 tothe apertured spring metal fuse-mounting clip 29. The diagonal leg 26lies on the diagonal surface 30 on the rear face of the block 12. Therivet extends through hole 31 extending from the rear face to the bottomwall of well 95.

The other fuse-mounting clip 32 is also made of spring metal and isseated at the opposite end of the well 95. It is connected conductivelywith the terminal post 16 by a rivet 33 which extends through theapertured ear 34 of the terminal bracket 35, the latter having mountedthereon a bolt 36 with a wire-holding nut 37. An insulating gasket 38with an apertured car 39 lies on the bottom wall of the recess 40 whichextends diagonally into the rear face from the side 41 of the block 12.The terminal post 16 is thus conductively connected with the blade 14via the fuse 42 and its fuse-mounting contacts 29 and 32. The gasket 38lies between the terminal post 16 and the contact blade 14 and itsdiagonal leg 26. It shields the latter against accidental contact by thewire attached to terminal post 16 and also prevents conductive foreignmaterial from accidentally bridging the gap therebetween.

The other blade 15 projects through passage 23, the rearward end ofwhich intersects a recess 43 which opens into the rear face edge portion44 and the rear portion of the side wall 45 of the block 12. The wall 46of recess 43 is slotted for the purpose of receiving one edge of thebase 47 of the blade 15. The bolt 49 and nut 48 serve the purpose ofclamping a wire to the terminal post 17. The arched portion 50 of thethird wall of the recess 43 accommodates the projecting end of the bolt,the slotted head of which isaccessible through the slotted opening inthe side wall 45.

The terminal post 19 of the ground pin 18 is seated in the same mannerin a recess 51 of like configuration to the recess 43 with an edge ofthe base 52 seated in the slot 53. The wire clamping nut 54 is threadedon the bolt 55, the projecting end of which is accommodated by thearched portion 56.

The block 12 has a rear cap 57 composed of a rear. cover plate 58 andside walls 59 and 60 dimensioned to enclose the two open sides of therear corner notch 61 of the block 12.

The cover plate 58 has a pair of apertures 62 and 63 for passage of thetwo wires to be connected to the terminal posts 16 and 17. A shorttubular member 64 serves as a passage for the grounding wire to beconnected to the terminal post 19.

The block 12 and its rear cap 57 are held in the hollow housing 11 bybolts 64 and 65, the shanks of which extend through countersunk passages66 and 67 in the block 12 and apertures 68 and 69 in the cover plate 58.The threads at the ends of the shanks are threaded in integrally moldedtubular columns 70 and 71 formed in two inner corners of the rearwardportion of the housing 11. The bolts 64 and 65 hold the cover plate 58against an inner, peripheral lip 72 extending along the inner faces ofthe four sides of the rear portion of the housing 11.

The hollow housing 11 has at its rearward end an electrical cable orcord clamping unit 73. A half section 74 thereof is molded integrallywith the housing 11. This section has solid side portions 75 and 76 withrespective bolt-receiving passages 77 and 78. Its midportion has abevelled, semi-circular opening 79 in its clamping face 80. Anelectrical cable or cord passes through the semi-circular opening 79 andis gripped on one side by the relatively sharp, bevelled edge of theopening 79 when the removable clamp section 81 is drawn against thecable by bolts 82 and 83.

The removable clamp section 81 is a molded plastic body having end wells84 and 85 for receiving said bolts. Its clamping face 86 has planar endfaces 87 and 88 with bolt passages 89 and 90 connecting said faces andthe respective wells 84 and 85. At the midportion of the face 86 is arecess or well 91, the front and rear edges of which have arcuate, cableor cord gripping walls 92 and 93 projecting outwardly therefrom. Thesewalls oppose and coact with the semi-circular passage 79 in the securegripping of electrical cables or cords of various diameters.

The fuse-mounting well 95 has a cover plate 96 which is movable into andout of covering relationship with relation to the well. The cover has afree end 97 which may overlie or cover, in the well-covering position,the well and an offset shoulder 98' (FIG. 3) in the face of the frontface 13. Its narrower neck 98 provides a notched edge portion 99 inwhich the blade 14 is positioned with the cover plate in well-coveringposition (FIG. 2). An arm 100 projects laterally from the base of thecover plate, the arm being pivotally joined at its base by a plastic pin101 having its end deformed into a rivet-like head. The base of the armlies in an offset corner 102 in the front face 13 (FIG. 4) whereby thefront surfaces of the cover plate, its neck and its arm aresubstantially flush with the plane of the front face 13.

As can be seen fron FIGS. 2 and 3, the swingable cover plate 96 and theposition of the fuse-mounting well 95 along one side of the front face13 gives ready, convenient access to the fuse 42 for its inspection orreplacement by simply swinging the cover plate 96 to the position shownin FIG. 3. Removal of the fuse cannot be done without removal of theplug from the receptacle. It is not necessary, as is the case withprevious known fused plugs, to remove completely any part of the plug,e.g., a front cover plate or its dielectric housing, to gain access tothe fuse.

The back-wiring feature of the invention allows the plug to be wired byremoving the blade-mounting body 12 and its rear cap 57 from the hollowplug body 11, e.g., as shown in FIG. 4. The respective bolts of theterminal posts are loosened. The wires of the cable or cord are strippedof their insulating sheath to a depth about equal to the depth of therespective wells or recesses in which the respective terminal posts aremounted. The bare wire ends are inserted through the respectiveapertures 62, 63 and 64 in the rear cap 57 and pass between therespective nuts and the terminal post portions 35, 47 and 52. The boltsare thereupon turned by a screwdriver to securely clamp the wires on therespective terminal posts.

The back-wiring feature provides complete isolation of the respectiveends of the wires from each other. Each bare wire end is located in awell or recess with dielectric material separating the wells orrecesses. This arrangement provides one very safe wiring arrangementwhich guards against accidental short-circuiting between wires in theplug, voltage leakages across wires in the plug and the like.

The configuration and orientation of contact blades 14 and 15 and theoptional ground pin 18 on the front face 13 is but one type of manywhich may be used. Other configurations and orientations for contactblade and ground pins of the non-locking or locking type (such as thoseapproved by the National Electrical Manufacturers Association forvarious voltages and amperages) may be used instead of that shown in theillustrated embodiment.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the form herein disclosed being a preferred embodiment for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. A dead front, back-wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in an offset segment of said front face, said offset segment andthe well therein extending longitudinally across one side of said face,fuse means in the circuit of one blade, said fuse means includingfuse-mounting clips in said well, and a thin plate cover member ofdielectric material swingably mounted on said front face and movableinto and out of covering relationship with relation to said well andlying flush with said front face when said plate is swung to overliesaid offset segment and the well therein.

2. An electrical plug as claimed in claim 1, said thin plate beingconnected by pivot means in said offset segment to said front face.

3. An electrical plug as claimed in claim 2, said a thin plate having aprojecting arm, and said pivot means being a pin pivotally connectingsaid arm to said front face, and said arm lying flush with said frontface and said plate when said plate is swung to overlie said offsetsegment and the well therein.

4. A dead front, back-wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in and extending longitudinally across one side of said frontface, said fuse means including fuse-mounting clips in said well, a slotextending transversely across a side wall of said well, and one of saidblades being mounted in said slot and extending across said side wall.

5. A dead front, back wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in said front face, fuse means in the circuit of one blade, saidfuse means including fuse-mounting clips in said well, said fusemounting clips being a pair of spaced, fuse-mounting clips mounted insaid well, a plurality of recesses in the rearward portion of saidblade-mounting body, means mounting one of said blades in one of saidrecesses in electrical contact with one of said clips, a terminal postwith wire-clamping means mounted in one of said recesses by meansproviding electrical contact with the other of said clips, and the otherof said blades extending through said body and having a rearwardterminal post positioned in another of said recesses.

6. An electrical plug as claimed in claim 5, said well being locatedalong one side of said front face, a slot extending transversely acrossa side wall of said well, and said one of said blades being mounted insaid slot and extending across said side wall.

7. A dead front, back-wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in said front face, fuse means in the circuit of one blade, saidfuse means including fuse-mounting clips in said well, said one of saidblades having a laterally extending base portion seated in a recess inthe rearward portion of said body directly behind said well, an aperturethrough said body connecting one end of said well and said recess, and ametal fastener in said aperture and connecting and mounting onefuse-mounting clip in said well and said base portion in said recess.

8. An electrical plug as claimed in claim 7, a terminal post mounted ina further recess in the rearward portion of said body in spaced relationto said one of said blades and its base portion, a second aperturethrough said body connecting the other end of said well and saidlast-mentioned recess, and a second metal fastener in said secondaperture and connecting and mounting another fuse-mounting clip in saidwell and said terminal post in said last-mentioned recess.

1. A dead front, back-wired electrical plug with a frontaccessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in an offset segment of said front face, said offset segment andthe well therein extending longitudinally across one side of said face,fuse means in the circuit of one blade, said fuse means includingfuse-mounting clips in said well, and a thin plate cover member ofdielectric material swingably mounted on said front face and movableinto and out of covering relationship with relation to said well andlying flush with said front face when said plate is swung to overliesaid offset segment and the well therein.
 2. An electrical plug asclaimed in claim 1, said thin plate being connected by pivot means insaid offset segment to said front face.
 3. An electrical plug as claimedin claim 2, said a thin plate having a projecting arm, and said pivotmeans being a pin pivotally connecting said arm to said front face, andsaid arm lying flush with said front face and said plate when said plateis swung to overlie said offset segment and the well therein.
 4. A deadfront, back-wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in and extending longitudinally across one side of said frontface, said fuse means including fuse-mounting clips in said well, a slotextending transversely across a side wall of said well, and one of saidblades being mounted in said slot and extending across said side wall.5. A dead front, back wired electrical plug with a front-accessible fusecomprising a hollow plug body of dielectric material, a blade-mountingbody of dielectric material mounted in one end of said hollow plug body,the blade-mounting body having electrical contact blades projecting fromits front face, means on the rear of said blade-mounting body forconnecting said blades to current wires of an electrical cord or cable,a well in said front face, fuse means in the circuit of one blade, saidfuse means including fuse-mounting clips in said well, said fusemounting clips being a pair of spaced, fuse-mounting clips mounted insaid well, a plurality of recesses in the rearward portion of saidblade-mounting body, means mounting one of said blades in one of saidrecesses in electrical contact with one of said clips, a terminal postwith wire-clamping means mounted in one of said recesses by meansproviding electrical contact with the other of said clips, and the otherof said blades extending through said body and having a rearwardterminal post positioned in another of said recesses.
 6. An electricalplug as claimed in claim 5, said well being located along one side ofsaid front face, a slot extending transversely across a side wall ofsaid well, and said one of said blades being mounted in said slot andextending across said side wall.
 7. A dead front, back-wired electricalplug with a front-accessible fuse comprising a hollow plug body ofdielectric material, a blade-mounting body of dielectric materialmounted in one end of said hollow plug body, the blade-mounting bodyhaving electrical contact blades projecting from its front face, meanson the rear of said blade-mounting body for connecting said blades tocurrent wires of an electrical cord or cable, a well in said front face,fuse means in the circuit of one blade, said fuse means includingfuse-mounting clips in said well, said one of said blades having alaterally extending base portion seated in a recess in the rearwardportion of said body directly behind said well, an aperture through saidbody connecting one end of said well and said recess, and a metalfastener in said aperture and connecting and mounting one fuse-mountingclip in said well and said base portion in said recess.
 8. An electricalplug as claimed in claim 7, a terminal post mounted in a further recessin the rearward portion of said body in spaced relation to said one ofsaid blades and its base portion, a second aperture through said bodyconnecting the other end of said well and said last-mentioned recess,and a second metal fastener in said second aperture and connecting andmounting another fuse-mounting clip in said well and said terminal postin said last-mentioned recess.